Gaseous discharge ballast and system



Aug. 21, 1962 A. E. FEINBERG 3,050,659

GASEOUS DISCHARGE BALLAST AND SYSTEM Filed April e 1966 a Sheets-Sheet 1 Qmmega Aug. 21, 1962 A. E. FEINBERG GASEOUS DISCHARGE BALLAST AND SYSTEM 3 Sheets-Sheet 2 Filed April 6, 1960 z 2 z 0 v 3 2 D .|ll!\ 0 T0 IIHII L 22 .vzlH w 2 a V PM 0 w ml 9 P 5 4; W 1 0 2 M M a 4 my QQerZTWe I afiaz/vaeg IIII" Aug. 21, 1962 A. E. FEINBERG 3,

GASEOUS DISCHARGE BALLAST AND SYSTEM Filed April 6, 1960 5 Sheets-Sheet s 564 F Dc LINE r100 n uo'ou'o (I-Hino'ofl Q2 1) 150 W 96 7 LINE 6g p2 6 fig LINE r 10.2 Q AE United States Patent 3,050,659 GASEOUS DISCHARGE BALLAST AND SYSTEM Albert E. Feinherg, Chicago, Ill., assignor to Advance Transformer Co., Chicago, Ill., a corporation of Illinois Filed Apr. 6, 1960, Ser. No. 20,412 27 Claims. (Cl. 315-257) This invention relates generally to apparatus for use in the ignition and operation of gaseous discharge devices and particularly is concerned with circuits, ballast structures and systems energized from conventional A.C. lines to provide the high ignition voltages and low operating voltages for such gaseous discharge devices.

As well-known, gaseous discharge devices ignite at voltages which are substantially higher than the voltages at which the discharge through such devices can be sustained. The impedance of a gaseous discharge device before the ionization of its gas commences is quite high, but once the discharge starts, the impedance drops to a very low value, and if the device .is not in some way prevented from passing the high current which results, it will destroy itself. In apparatus for the ignition and operation of gaseous discharge devices, therefore, there are at least three basic problems which all such devices must solve. The first is ignition-the provision of a high voltage sufiicient to result in ionization of the gaseous atmosphere within the discharge device. The second is operationthe voltage which is applied to the gaseous discharge devices must drop to a lower value so that the current which flows through the discharge device is rated, that is, the value for which the device is designed. The third is ballasting-the apparatus must provide impedance to flow of current which will prevent the ignition of the discharge device fronr destroying itself.

The apparatus which will be described herein is especially adapted for and intended to be used in connection with fluorescent lamps of a conventional construction, although not limited thereto. Fluorescent lamps are normally constructed as elongate tubular envelopes sealed on both ends by metal caps, with suitable electrodes protruding. A filament is usually provided at each end the purpose of which is to provide the source of electrons during ignition (and at times during operation) and the hot spot from which the arc discharge will extend to the opposite filament. Further mention will be made of the filaments.

The interior of the envelope is provided with an inert gas such as argon and a few droplets of mercury while the inner walls are coated with phosphors which fluoresce under bombardment of the discharge radiation. The gas is usually at low pressure, and the principal source of the ultra-violet radiation required to fluoresce the phosphors is caused by ionization of the mercury vapor within the envelope.

There are many types of fluorescent lamps, with many different ratings and requirements of ignition and operation voltage. Some gaseous discharge devices ignite instantaneously when the ignition voltage is applied across their filaments, these lamps being called instant start lamps. The ignition voltages and operating voltages are relatively higher than most of the other types. The filaments of these lamps are short-circuited, and hence each 3,050,659 Patented Aug. 21, 1962 end cap has only one electrode or pin. Other fluorescent lamps ignite at relatively lower voltages and have current flowing in their filaments continuously. These lamps ignite quite rapidly, and are called rapid start lamps, requiring somewhat lower voltages for ignition and operation than the instant start lamps of substantially the same light output. The standard fluorescent lamp which has been in commercial use longer than any of the others and which is used practically universally all over the world is the so-called pre-heat start lamp which requires less ignition and operation voltage than either of the others mentioned.

The pre-heat start lamp is provided with a filament in each end thereof, the terminals of which are brought out to the pair of pins protruding from each end cap. The filaments of the pre-heat start lamp are designed to conduct current for only a short time, and hence in any apparatus designed for use in connection with such fluorescent lamps, means must be provided for discontinuing the current flowing in the filaments when the lamp has ignited. The result of continuous flow of current in the filaments is a rapid decrease of the ability of the filament to produce electrons, followed by its deterioration.

The conventional circuit of a preheat start lamp includes a switch which is closed when the lamp is to be started and thereafter opened when the arc has been struck. The switch closes a circuit which includes both of the filaments of the lamp and heats them to incandescence so that clouds of electrons are driven off in the vicinity of the filaments. This decreases the voltage which is required to strike the arc; hence, when the arc strikes, the starting switch is by-passed by the current flowing through the lamp. The are is struck by opening the switch so that there is a high voltage transient caused by the collapse of the field in an inductor connected in the circuit.

The modern apparatus utilizes a thermostatically operated element disposed in a small bottle of gas that glows when starting voltage is applied across its electrodes. This glow heats the element which closes the electrical switch in series with the filaments. As the current passes through the switch the glow is extinguished and the cooling of the thermostatic element once more opens the switch. The resulting surge ignites the are which then bypasses the bottle of gas, the voltage across the lamp dropping to a value which is insufficient to sustain the glow discharge in the bottle. These starting devices are wellknown and are sold commercially as starters for fluorecent lamps.

As previously mentioned, perhaps the most universally utilized fluorescent lamp in the world today is the 40 watt pre-heat start lamp. This lamp requires a voltage of approximately 200 volts to ignite the arc thereof, and a sustaining voltage of the order of volts once the discharge has commenced. Since most of the locations where these lamps are used have power sources of 118 volts at frequencies of 50 to 60 cycles, obviously some means is required to raise the line voltage sufficient to ignite these lamps and sustain their operation. The apparatus which is used to ignite and provide the operation voltages for these lamps includes a transformer to increase the line voltage. The form of apparatus (hereinafter called a ballast or ballasts) most commonly used for these lamps is connected to serve two lamps, one operated with a leading current, and the other with a lagging current. This eliminates the stroboscopic effect caused by the variation of light output with the alternation of the source. Lamps operated in unison will give such stroboscopic effect. The use of apparatus operating a pair of lamps with leading and lagging currents respectively in the lamps also promotes good power factor for the effect of the apparatus and lamps upon the line.

The apparatus above described is called a lead-lag ballast. It usually consists of an iron core of suitable construction, which mounts a primary winding that has two secondaries each connected into auto-transformer relationship with the primary winding across a lamp. Thus, there are two parallel circuits connected with the single primary winding, each circuit including a lamp and a secondary winding. In addition, one of the circuits includes a capacitive reactor so that the current flowing therein is leading. Since the phase of the current flowing in the other circuit is controlled by the inductive reactance of the secondary, it is lagging. With leading and lagging currents flowing in the primary winding, the power factor of the circuit will be very high. Often, instead of a primary winding alone, there may be an additional or autotransforrner winding or windings, so that the voltage of the source is additionally raised.

A typical lead-lag ballast will be built upon an iron core formed of larninations of electrical steel assembled by rivets or clamps in a suitable stack or stacks. The core may be of the so-called shell variety in which there is a rectangular frame portion and a center winding leg disposed in the frame portion between the bridging ends. The center winding leg mounts all of the windings, and may be either forced into its position in the case of a unitary frame member, or may be disposed in that posi tion and held in place by clamps where the outer framing portion is formed of two or more parts. Another form of core is comprised of L-shaped parts arranged face to face, and each winding is formed of a pair of coils disposed juxtaposed relative to one another on respective legs of the core formed by the elongate portions of the L-shaped parts. The primary winding is disposed in the center of the elongate core, separated from the respective secondaries. The leakage reactance required for the lag secondary is greater and hence its coupling with the primary winding is less than that of the lead secondary. The coupling is adjusted either by gapped shunts or simply by spacing the windings apart.

The transformer and its core as well as the condenser which is in series with the lead secondary winding are all disposed in a suitable metal canister and immersed in some potting compound such as pitch, with the electrical leads protruding from the ends of the canister and a diagram carried on the canister showing the connections with the lamps. In some instances, the condenser is intended to be external of the canister.

The lead-lag ballast described above is a very economical and advantageous device. It is a structure which is formed on a unitary core with a minimum amount of handling and labor required to assemble it; it has a minimum of copper and steel; it is small in size and economical to manufacture, store and ship. It does not draw high currents, provides good power factor, runs cool, is not noisy.

The lead-lag ballast above referred to provides these advantages when operated on a line voltage of 118 volts with 40 watt lamps.

The problems with which the invention herein is concerned arise when it is desired to operate the low wattage lamps from sources of electric power whose voltage is of the order of 200 volts AC. and more. One might assume that the problem of transformation having been eliminated, the resulting structure is easier to devise than the 4 lead-lag ballast, but this is found to be an erroneous assumption.

Heretofore attempts made to use the lead-lag configuration above described have failed. It has been found that Where a primary Winding is built for a high line voltage of say -220 volts AC. and the secondaries energized by using a tap on the primary winding to achieve the 118 to 120 volt input required for substantially the same operation as in the conventional lead-lag transformer, the primary winding developed such high temperatures that the structure was not feasible.

Accordingly, the desirabilities of the unitary structure have in the past been given up and in place thereof, ballast artisans have gone to the use of two separate chokes, each mounted on its own core. Each choke is in series with one of the lamps and one of the lamps is additionally in series with a capacitive reactor. The source is connected across both of the lamp circuits, the latter being in parallel. Conventional core structures for the chokes have been used, comprising E-shaped laminations, either with other E-shaped larninations or with I-shaped laminations, and various other configurations.

The invention herein achieves a structure for igniting and operating the low wattage lamps such as the 40 Watt pre-heat start lamps from relatively high voltage sources, such as 220 volts A.C. lines or better, which has all of the advantages of the unitary lead-lag ballast described above and none of the disadvantages of the multiple choke system. This forms the principal object of the invention.

Another object of the invention is to provide a unitary ballast construction and system for the ignition and operation of gaseous discharge devices in which a plurality of inductors are mounted on a unitary core and have common magnetic circuits which advantageously prevent excessive starting currents, keep the heat and losses generated at low values, provide a small and compact ballast structure, which operates at a very high power factor.

An important object of the invention is concerned with the economy of the structure of the invention in that the core used for the construction of a very efficient leadlag ballast intended for use with a relatively low voltage source can be used to build a ballast for the same gaseous discharge devices but energized from a source of substantially higher voltage.

Still other objects of the invention are concerned with the construction of a novel ballast which has a plurality of inductively reactive elements mounted on a unitary core, and which provides a novel and improved structure and system for igniting and operating gaseous discharge devices in a lead-lag circuit, over andabove the achievement of the object immediately above.

Other objects of the invention are concerned with the provision, in a device of the character described, of means for balancing the currents in the lamps; means for compensating for low current in the leading circuit on starting; means for decreasing the number of turns required in the ballast below that required with chokes.

Many other objects are inherent in the invention and will be appreciated as a description of the invention proceeds hereinafter in some detail. In the description, several forms of the invention are described, all of which are by way of example and not limitation, and which indicate the preferred form of the invention. The several forms of the invention, as well as the known structures in this art, are all illustrated in the drawings appended hereto, the description being directed to a complete discussion of these illustrations in order that those skilled in this field may understand fully the advance which has been made in the arts and sciences.

In the several figures of the drawings, like characters of reference are used Wherever feasible for the purpose of designating the same or equivalent elements or components in the several drawings.

In the said drawings:

FIG. 1 is a circuit diagram of a system for igniting and operating a pair of gaseous discharge devices from a relatively high voltage source, in which the ballast illustrated is constructed in accordance with the invention herein.

FIG. 2 is a sectional view through an electromagnetic core which is suitable for mounting the inductively reactive elements (hereinafter called inductors) of the invention as illustrated in FIG. 1.

FIG. 3 is a semi-diagrammatic illustration of a system for igniting and operating a pair of gaseous discharge devices using the circuit of FIG. 1 but in which the core mounting the inductors is formed of L-shaped laminations arranged face to face.

FIG. 4 is a circuit diagram of a modified form of the invention comprising a variation of the circuit of FIG. 1.

FIG. 5 is a sectional view through another electromagnetic core which is suitable for mounting the inductors of the invention.

FIG. 6 is a circuit diagram of a conventional lead-lag system and ballast for operating a pair of lamps from a low voltage source, the transformer capable of being mounted onthe cores of any of FIGS. 2, 3 or 5.

FIG. 7 is a circuit diagram of a lead-lag arrangement in which separate chokes are used for each of the lamp circuits, the same comprising a conventional system for igniting and operating the lamps from a relatively high voltage source.

FIG. 8 is a sectional view through a core of double E construction suitable for mounting one of the chokes of FIG. 7, the same illustrating the prior art.

FIG. 9 is a sectional view through a core of E I construction also illustrative of the prior art.

FIGS. 10, 11, 12 and 13 are circuit diagrams of modified forms of the invention illustrated in FIG. 1.

The invention is characterized by the provision of a unitary core which mounts three inductors, one of which is connected in common with the other two, the latter two each being respectively connected in series with a lamp, one of the lamps having a series capacitive reactor in its circuit. The common inductor is disposed in the center of an elongate winding leg, with the other two inductors on opposite sides thereof, separated by shunting means, either in the form of gapped magnetic shunts or large spaces. The inductor in the lamp circuit which includes the capacitive reactor will carry a leading current, while the other inductor carries a lagging current. The entire circuit is connected across a line for power. By arranging the inductors so that the flux produced in the core by the common inductor is in opposition to the flux in the core produced by the other inductors, the advantages of low starting current, low heating losses, low number of turns and good efliciency are achieved.

In order to appreciate the unobvious nature of the invention and to visualize the differences between the invention and the structures which have heretofore been used, attention will be invited directly to FIG. 6, 7, 8 and 9 and indirectly to FIGS. 2, 3 and 5. The latter three figures illustrate cores which can be used without any material or substantial change either in the construction of prior ballasts or the structure of the invention. This emphasizes the importance of the advance since it enables a manufacturer to exercise great economy in the manufacture of the apparatus.

FIG. 6 illustrates a lead-lag ballast structure connected to ignite and operate a pair of low wattage gaseous discharge lamps of the pre-heat variety from a relatively low voltage source requiring some transformation in order to enable ignition of the lamps. The ballast is designated and it comprises a core 22 which may be any one of those illustrated in FIGS. 2, 3 or 5, mounting a primary winding P, a secondary winding 8;, and a secondary winding S The primary winding P is in the center of the core 22 and is separated from the secondary winding 8;, 'by a shunt 24 which may have air gaps at 6 26 (see FIGS. 2 and 5). Winding P is separated from the secondary winding S by a shunt 28 which may have air gaps at 30. The shunt 28 is smaller than the shunt 24 because less leakage reactance is required for the leading circuit, winding S being the lead secondary winding.

The lead secondary winding S is connected through a series capacitor C in lead 32 to one pin of the pair on the right hand end of the gaseous discharge lamp D One of the left hand pins connects by way of the lead 34 to the lead 36 which is a conductor extending from one terminal of the primary winding P to the line terminal 38. The remaining pins on opposite ends of the lamp D are connected in a by-pass circuit 40 through some form of starter switch designated S. It will be appreciated that the lamps of this circuit are of the preheat variety.

The right hand terminal of the primary winding P is connected by way of the lead 42 to the other line terminal 44 so that full line voltage is applied across the primary winding. The right hand terminal of the primary winding P provides a junction 46 to which are connected the left hand terminal of the winding S and the right hand terminal of the winding 8 The left hand terminal of the secondary winding S connects by way of the lead 48 to the lamp D one of whose left hand pins is connected to lead 34. The remaining pins of the lamp D are also connected in a starter circuit as at 50.

Through the auto-transformer connection at junction 46 each of the secondaries of the ballast 20 is connected additively with the primary winding P so that the sums of voltages across the primary winding P and the respective secondaries S and 8;, are added for igniting the respective lamps D and D The circuit is too well-known to require discussion with any further detail. Saturation of the core in the vicinity of the secondary winding S may be relieved by means of a suitable gap such as at 52 (FIGS. 3 and 5) or a slot such as at 54 (FIG. 2). Shunts may be replaced by spaces such as in FIG. 3.

As explained, if it is desired to operate and ignite the lamps from a higher voltage source, such as one having about twice that of the line 3844, the ballast 20 is not suitable. In its place, the system or apparatus which is illustrated in FIG. 7 has been used. This apparatus which carries the general designation 60 utilizes a pair of sepa rate chokes which are designated L and L having a common terminal 62 connected to the line 64. The choke L is in series with the discharge device D through the lead 66 which connects with one of the right hand pins of the discharge device D One of the left hand pins of the discharge device D is connected to the lead 68 which in turn extends to the other terminal 70 of the line. It will be appreciated that the line 6470 in this case is of higher voltage, such as for example 220 volts A.C. A starter circuit 50 is connected across the discharge device D to the others of the pins of said device.

The choke L is connected in series with the discharge device D by way of the lead 72 having a series condenser C therein. A left hand pin of the discharge device D also connects to the lead 68, and there is a starter circuit 40 across the two opposite and remaining pins of the discharge device D The apparatus 60 as will be seen comprises a pair of parallel circuits each of which has a separate choke L or L in order to provide the anti-stroboscopic effect desired. The production of such apparatus is expensive and results in a large package since each of the chokes must be mounted on a separate core. These cores, as stated above, may take many different forms. For example, in FIG. 8 there is illustrated a core designated 74 which is formed of right and left hand E-shaped laminations 76 and 78. These laminations are arranged in stacks and either clamped, riveted or otherwise fastened together to provide gaps at 80, either in the center or top or at both locations of the chokes between the two E-shaped laminations. The winding of the choke is disposed in the windows formed between the E-shaped laminations. Obviously two of these formations or core assemblages 74 are required for each of the apparatus 60. This requires multiple handling in manufacture, etc.

Another form of core designated 82 is illustrated in FIG. 9. In this case the laminations comprise E-shaped laminations as shown at 84 and I-shaped laminations as shown at 86. The gaps which are required in order to provide the reactance after current flows through the winding are shown at 88. Again, as in the case of the choke core 74, it is necessary that there be two of these assemblages in order to provide for ignition and operation of the fluorescent lamps D and D in the circuit shown in FIG. 7.

The apparatus which is shown in FIG. 1 is designated generally by the reference character 90. There is illustrated a system for igniting and operating a pair of gaseous discharge devices D and D which may be 40 watt pre-heat fluorescent lamps, the system being energized from an A.C. source 64 and 70 of relatively high voltage, say of the order of 220 volts or more. This system as shown embodies the invention. A core 22 is provided of the type illustrated in FIGS. 2, 3 and 5. Mounted on the core 22 are three windings, designated L L and L each of these windings comprising an inductor in the igniting and operating circuit. The inductor L is disposed in the center of the core 22 and the inductor L is mounted to the left as shown in the view, separated from the inductor L by means of a shunt 24 which may have gaps 26 or may simply be a large space as shown in FIG. 3. The inductor L is disposed on the right hand end of the core and it is separated from the inductor L by means of the shunt 28 which may have air gaps 30 or a space.

This arrangement minimizes the coupling of the windings L and L relative one another, which is advantageous since it will be appreciated that lagging current will be flowing in the winding L and leading current in the winding or inductor L The left hand terminal of the inductor L is connected to the line 64 by way of a lead 92, whereas the right hand terminal of the inductor L forms a junction 94- which is common to all three of the inductors. It will be seen that the inductor L has its right hand terminal connected to the junction 9'4 by way of the lead 96 and the right hand inductor L has its right hand terminal also connected to the junction 94 by way of a lead 98. The inductor L has its terminal connected to one of the right hand pins of the discharge device D by way of the lead 100. One of the left hand pins of the discharge device D connects to the line terminal 70 by way of a lead 102. A shunting circuit including a starter device designated S is shown at 50, shunting the lamp between the other pins and completing a circuit through the filaments which are disposed at each end of the discharge device D The left hand terminal of the inductor L is connected to one of the right hand pins of the discharge device D by way of a lead 104 having a series condenser C therein. The left hand pin of the discharge device D connects with the line terminal 70. There is also a shunting starter circuit 40 provided across the lamp D The inductors L L and L are disposed upon the core 22 in such a manner that the magnetomotive forces which are generated due to the passage of current in L and L are in opposition to the magnetomotive force which is created by the passage of current through the common inductor L Specifically, with current flowing in each of the inductors L and L in the directions indicated by the arrows of FIG. 1, the induced fluxes in the respective parts of the core 22 will oppose one another. This will force the flux to tend to pass through the shunt 24 and thereby develop considerable leakage reactance. Consid- 8 ering now the two inductors L and L it will be seen that the arrows, representing flow of current, are opposed to one another in FIG. 1 and hence the magnetomotive force or flux which is generated by the passage of current through these two inductors would also be in opposition, causing the flux to pass through the shunt 28 and thereby developing leakage reactance thereat. As in the case of the lead-lag transformer the amount of leakage reactance required by the inductor which will carry leading current is less and hence the size of the shunt 28 is also smaller than the size of the shunt 24.

It is believed that the concept of utilizing inductors in the relationship which has been described is novel, the air gaps in the shunts being used as reactance gaps and the flux being forced to traverse these shunts by virtue of a bucking arrangement between inductors. The flux in the vicinity of the inductor L opposes the flux in the vicinity of each of the inductors L and L in order to provide the desired result, and yet because of the location of the inductors L and L on opposite ends of the core, there will be a minimum of coupling therebetween, not upsetting the operation or starting of the device.

The structure described provides flux densities which are not excessive. Several very important advantages are achieved through this structure and this relatively low flux density. in the first place, the number of turns re quired in order to give satisfactory ignition and operation has been reduced, especially in the lead inductor L This cuts down on wave shape distortion and decreases the need for the presence of slots such as 54 or gaps such as 52 designed to correct Wave shape and decrease saturation. As a matter of fact, in many structures these slots or gaps may be eliminated entirely. Decreased number of turns decreases the copper requirements. Decrease in the voltages occurring in the apparatus also decreases the requirements of the condenser C and therefore also decreases the cost and expense of building this apparatus.

In operation of the apparatus in FIG. 1, it will be appreciated that leading current will be flowing through the inductor L and its discharge device D while lagging current will be flowing through the inductor L and its gaseous discharge device D The currents flowing in the inductors L and L will both be flowing in the common inductor L and since the phase is opposite there will be neutralization with the result that the current drawn by this device is a substantially in-phase current with a very high power factor.

It will be noted, therefore, that the effect of using the apparatus herein is the same as in the case of a transformer structure such as illustrated in FIG. 6, but this device is not a transformer as it is understood.

A ballast was constructed in accordance with the teachings of the invention for operating and igniting a pair of 40 watt pre-heat start fluorescent lamps from a 220 volt 60-cycle A.C. line. This structure was based upon a core 22 as illustrated in FIG. 5. The overall length of the lamination was 5% inches, the overall width was 2% inches, and the remaining dimensions may be determined from the figure proportionally relative to those given. The laminations were of electrical steel, and were stacked to a height of approximately of an inch. The inductor L had 975 turns of No. 29 gauge wire, the inductor L had 845 turns of No. 29 gauge wire, and the inductor L had 1,150 turns of No. 29 gauge wire. No. 29 gauge wire has an overall diameter including a coating of insulating enamel of approximately .0122 inch, the enamel being about .001 inch in thickness.

The condenser C was a 3.25 microfarad condenser rated at 330 volts. In normal operation, the lead lamp had a current flowing therein of .395 ampere, the lag lamp had a current flowing of .325 ampere and the current drawn from the line was .405 ampere at a power factor of percent. The voltages across the inductors were: across the inductor L volts, across the inductor L 56 volts and across the inductor L 123 volts. Voltage measured across the condenser during operation was 320 volts. The flux density in the vicinity of the three inductors was, in the vicinity of the inductor L approximately l3.9 kilogauss, in the vicinity of the inductor L approximately 6.9 kilogauss, and in the vicinity of the inductor L 11.2 kilogauss.

This device gave satisfactory operation at temperatures well within those considered acceptable for normal operation of ballasts.

In building the ballast for commercial sale, as stated, the core with its mounted windings and the condenser C are all placed in a canister with leads protruding and suitably identified. Radio interference condensers and safety resistors are also included although not shown in the diagram. This device is potted in a metal canister. In assembling the device, the same techniques may be used as in assembling transformers which are to be used in gaseous discharge circuits. For example, in the case of the cores 22 of FIGS. 2 and 5, the central winding leg 110 is normally punched from a rectangular blank thereby providing the outer framing part 112 and the windows 114, 116 and 118 which are located along the length of the core and disposed on opposite sides of central Winding leg 1-10. Integral inwardly extending portions 121) and 122 form the respective shunts 24 and 28, although as shown here the central winding leg has outward projections 124 to cooperate with the projections 122. The windings are formed as somewhat cylindrical coils on rectangular tubes and these are slipped on to the central winding leg with the projections 124 assisting in positioning the respective coils after which the entire assemblage is forced into the framing part 12.

' In the case of the core 22 the ends of the central winding leg 110* form mating junctions at 126 and 128 with the respective left and right hand bridging parts of the framing part 112. In the case of the core in FIG. a similar mating junction is shown at 126 but a sharp protuberance on the right hand end of the central winding leg as shown at 130* engages a suitable notch 132 formed in the right hand bridging part in order to give rise to a bridged gap 52. Obviously many other structures of core are feasible.

It will be appreciated that most manufacturers of leadlag transformers can utilize the identical laminations for the construction of the ballast of the invention herein. This provides great economies in producing ballasts for use on high voltage lines for igniting and operating low wattage lamps.

The two cores 22 illustrated in FIGS. 2 and 5 are of the so-called forced core variety. The outer framing part 112 in each case is an integral rectangular member. The central winding legs and the outer framing parts are held in assemblage by means of grommets or rivets which are shown at 140. It is feasible to use cores of the type in which the outer framing portion is not formed as an integral lamination but may be made up of two or more parts. For example, a center winding leg having a T- shape may be assembled with outer side parts of L configuration using clamps. This type of core will operate with the invention in a satisfactory manner.

A very popular form of core which is well known throughout the world is illustrated in FIG. 3. This core 22 is formed of stacks of L-shaped laminations designated 142 which are arranged face to face but with the short arms of the L opposite. Instead of using single coil windings, each winding is divided into two equal coils which are disposed adjacent one another but on opposite legs of the transformer. Thus, as shown in FIG. 3, the inductor L in this case is divided in two and each of the resulting coils mounted on the respective legs with a connecting conductor 144. Likewise the inductor L is divided in two and has a connecting conductor 146 and the inductor L is divided in two and has a connecting conductor 148. As stated previously, the shunting of flux achieved in this structure by merely spacing the windings sufliciently apart to produce the desired leakage reactance. In all other respects, the circuit is identical to that of FIG. 1 and the reference characters applied to the identical parts. In the core 22 which is illustrated in FIG. 3, if a gap is desired in the vicinity of the inductor L which carries the leading current, it may be located at the junction 52.

In order to increase the starting current for starting the gaseous discharge device D in the lead circuit, compensators have been used in which a winding is coupled to the lead secondary of a transformer in order to have induced therein an additive current effective during starting. In the invention herein this may be accomplished by means of a fourth winding designated L in FIG. 4 which is closely coupled with the lead inductor L preferably Wound directly on the coil. In all other respects, the circuit of FIG. 4 which is designated is identical to that of FIG. 1.

The invention as described herein enables a great deal of flexibility in constructing ballasts for varying conditions. For example, the use of inductors of different numbers of turns and shunts of varying dimensions often gives rise to problems of balancing the current flow in the lamps. Obviously it is desirable that the identical current flow in each of the lamps so that the life of the lamps will thereby be increased.

In FIGS. 10, 11, 12 and 13, there are illustrated four ditferent arrangements of connections of the inductors to one another in order to obtain better balance between the lamp currents and to minimize the influence of the ignition of the lamps one upon the other which might occur during starting. In each case, the circuit is identical to the circuit of FIG. 1 with the exception that in each case one of the inductors L and L is connected to a tap on either of the other two windings.

In FIG. 10 the inductor L has its lead 96 connected to a tap 159 provided at the right hand end of the inductor L a relatively small number of turns from the right hand terminal of the inductor L In this case the right hand terminal of the inductor L is then connected directly to the right hand terminal of the inductor L In FIG. 11 the right hand terminal of the inductor L is connected directly to the right hand terminal of the inductor L while the right hand terminal of the inductor L is connected by way of the lead 98 to a tap 150 on the inductor L In each of the above cases it will be seen one of the inductors L and L which respectively carry the lagging and leading currents, is connected so that its current flows only in a portion of the inductor L while the current flowing in the other of these inductors L and L flows through all of the inductor L This obviously provides a means for controlling total flux and totfl current in the various parts of the apparatus.

In FIG. 12 the inductor L has its right hand terminal connected by way of the lead 96 to a tap 152 provided on the inductor L adjacent its right hand terminal. The right hand terminal of the inductor L is connected by way of the lead 98 directly to the right hand terminal of the inductor L With this structure, as will be seen, the current from both of the inductors L and L will flow through the common inductor L but in addition the lagging current from the inductor L will flow through a portion of the turns of the inductor L and thereby either neutralize current flow or flux produced by the winding L3.

In FIG. 13 the right hand terminal of the inductor L is connected directly to the right hand terminal of the inductor L by the way of the lead 96 while the right hand terminal of the inductor L is connected by way of a lead 98 to a tap 154 adjacent the right hand end of the inductor L In this case a portion of the leading current will be flowing through some of the windings of the inductor L In all of the structures which have been described in connection with FIGS. 10, 11, 12 and 13 adjustment of current balance in the lamps is achieved and better operation appears to be feasible. Whether this occurs by virtue of partial neutralization of current or flux, it is not known. It is pointed out, however, that this arrangement gives great flexibility in the design and construction of these ballasts for many diiferent conditions of operation and designs of ballast.

A successful structure similar to that of FIG. 11 was built using the lamination identical to that shown in FIG. 5. In this case the inductor L had 1,050 turns of No. 29 gauge wire, the inductor L had 780 turns of No. 28 wire and the inductor L had 470 turns of No. 28 wire. The same line voltage and the same lamps were used. The tap 150 was at 60 turns from the right hand end of inductor L The operating current through the lead lamp D was .395 ampere, through the lag lamp was .330 ampere, and the line current was .39 ampere at a power factor of 98 percent. The capacitor C was 3.7 microfarads, but was at a rated Voltage of 260 volts, being thereby substantially more economical than the condenser which was used in connection with the example described in FIG. 1. The total watts input was 84 and the voltages across the various windings were 172 volts across the inductor L 90 volts across the inductor L and 35 volts across the inductor L The flux density in the vicinity of the various inductors was: in the vicinity of the inductor L 17.1 kilogauss, in the vicinity of inductor L 12 kilogauss and in the vicinity of the inductor L 7.75 kilogauss. It will be noted that through the adjustment of the relationship between the windings it was possible to obtain a very high power factor which is a desirable efiect. It was of interest to note that the voltage across that portion of the inductor L which comprised only 720 turns was 98 volts at a flux density of 14.2 kilogauss, illustrating the effect of neutralization which may be achieved with adjustment.

In addition to other advantages, this invention is characterized by an absence of excessively high shorting currents. During starting the common inductor L carries inductive current primarily to augment the lagging inductor L in opposing the high surge of current which would tend to heat up the windings.

It is believed that the advantages and features of the invention have been fully explained in connection with the above specification of the drawings and that those skilled in this art will understand the manner of construction of the invention and operation and use thereof. It is desired to point out that a considerable variation in many of the details may be made without in any way departing from the spirit or scope of the invention as defined in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

1. A lead-lag ballast for igniting and operating a pair of gaseous discharge devices from an A.C. source which comprises an elongate iron core having three windings disposed along the length thereof, the center winding being spaced from the end windings, lead means connected to one end of said center winding for connecting said one end to one side of said source, one end of the first end winding having lead means for connecting same through one of said pair of gaseous discharge devices to the second side of said source, one end of the second end winding having means including a series condenser for connecting same through the second one of said pair of second gaseous discharge devices to said second side of said source, the second ends of all three windings being connected together to provide two parallel paths for current flowing in said center winding when connected to said source, said windings being mounted on said core with the flux of each end winding bucking the flux of the center winding to create leakage reactance between said center winding and each of said end windings.

2. A ballast as claimed in claim 1 in which one path includes all of said center winding and all of one of said end windings, while the second path includes a substantial part of the center winding and all of said other end winding.

3. A ballast as claimed in claim 1 in which one of said first and second end windings has a tap adjacent said second end thereof, said one path includes all of said one end winding and all of said center winding, and in which the second end of said other of said end windings is connected to said tap to form the second path having all of said center winding, all of said other of said end windings, and the tapped portion of said one of said end windings.

4. A ballast as claimed in claim 1 in which each winding has a terminal at its second end and all are connected together forming a common junction.

5. A lead-lag ballast for igniting and operating a pair of gaseous discharge devices from an A.C. source which comprises an elongate iron core having a central winding and having windings at opposite ends of said core separated from said center winding, said center winding having one terminal adapted to be connected to said source and the other terminal connected to a terminal of each of said end windings whereby current flowing in each of said end windings will flow also through said center winding, each of said end windings adapted to be connected in series with a gaseous discharge device, and one of said end windings being connected also in series with a condenser, said end windings being connected and disposed on said core for, respectively, creating bucking flux in opposition to flux established by said center winding.

6. A lead-lag ballast for igniting and operating a pair of gaseous discharge devices from an A.C. source and which comprises an elongate iron core, three inductors mounted on the core along its length and the two end windings having a common connection with the center winding and providing two separate circuits for connection to said pair of gaseous discharge devices respectively, a capacitor in the circuit of one winding, and means for connecting the circuits across said source whereby the currents flowing in each circuit will flow combinedly in said center winding, the windings being arranged so that the flux of the center winding bucks the fluxes of the end windings respectively.

7. A ballast as claimed in claim 6 in which there are high reluctance shunts between the center winding and each of said end windings and the shunt between the center winding and the end winding having said capacitor in its circuit is of lower reluctance than the other shunt.

8. A ballast as claimed in claim 6 in which the shunts are formed by portions of said iron core and have high reluctance gaps therein.

9. A lead-lag ballast for igniting and operating a pair of pre-heat start gaseous discharge lamps from an A.C. source which comprises, an elongate iron core having a center winding and end windings separated from said center winding with shunts between said windings, the center and end windings having a substantially common connection at one end of each of same, the second end of the center winding adapted to be connected to one side of said source, each end winding having means including leads for connecting a gaseous discharge lamp in series therewith and to the other side of said source, and a condenser in series with one of said end windings, substantially all of the current through each end winding being common to the current flowing in said center winding, and the windings being connected so that the flux of the center winding bucks the respective fluxes of the end windings.

10. A ballast as claimed in claim 9 in which there is a compensator winding on said core closely coupled with said one end winding having the condenser in series therewith and said compensator having lead means for con- 13 necting same with the gaseous discharge lamp of said one end Winding to aid the starting thereof.

11. A gaseous discharge lighting system adapted to be operated from an AC. line and including a leading circuit having a first gaseous discharge device, condenser and a first inductor connected in series, a lagging current circuit having a second inductor and a second gaseous discharge device connected in series therewith, said circuits being connected in parallel one with the other, a third inductor connected in series with both of said parallel circuits and together therewith being connected across said line, an elongate electromagnetic core mounting all three of said inductors with the third inductor disposed between the other inductors and with shunt means between said third inductor and each of said other inductors, the inductors being so Wound and disposed on said core to provide bucking flux between said third inductor and each of said other inductors so as to create leakage reactance in each of said shunt means during operation of said system.

12. A system as claimed in claim 11 in which said gaseous discharge devices each has a starter circuit shunting same, a compensator winding is mounted on said core closely coupled with said first inductor and in series with the starter circuit of said first gaseous discharge device.

13. A system as claimed in claim 11- in which all three inductors having a common junction joining one terminal of each.

14. A system as claimed in claim 11 in which an end terminal of said center inductor is connected to an end terminal of one of said first and second inductors, and a tap is provided short of said end terminal of said center inductor, and an end terminal of the other of said first and second inductors is connected to said tap.

15. A system as claimed in claim 14 in which said one of said first and second inductors is the first.

16. A system as claimed in claim 14 in which said one of said first and second inductors is the second.

17. A system as claimed in claim 11 in which an end terminal of said center inductor is connected to an end terminal of one of said first and second inductors, the latter having a tap, and an end terminal of the other of said first and second inductors is connected to said tap.

18. A system as claimed in claim 17 in which said one of said first and second inductors is the first.

19. A system as claimed in claim 17 in which said one of said first and second inductors is the second.

20. A gaseous discharge lighting system for igniting and operating a pair of gaseous discharge devices from a source of AC. voltage substantially higher than the operating voltages of said devices and which comprises, an elongate iron core having a center winding and first and second end windings each spaced from the center winding along the length of the core, with the separation between the center and second end windings less than the separation between the center and first end windings, one circuit connected across the source and comprising the center winding, said first end winding, and one gaseous discharge device, a second circuit connected across the source and comprising the center winding, said second end winding, a condenser and a second gaseous discharge device, the center Winding being common to both circuits, the windings being arranged such that the flux of the center winding opposes the flux of the other two windings whereby to provide leakage reactance between the center winding and the other two.

21. A system as claimed in claim 20 in which high reluctance shunts are disposed between windings.

22. In apparatus of the character described in which there are a pair of gaseous discharge circuits one carrying a leading current and one carrying a lagging current, an inductive device comprising an elongate iron core having a center winding and windings on the ends of said core and high reluctance shunts between said center winding and each of said end windings, one end winding adapted to carry the lagging current, the second end winding adapted to carry the leading current, the center winding being connected to said end windings common with both circuits and adapted to carry both said leading and lagging currents, a pair of electromagnetic circuits in said core linked together through said center winding, each electromagnetic circuit having the flux of an end winding and the flux of the center winding threading the same but with the fluxes in opposition whereby to create leakage reactance at said shunt of said magnetic circuit.

23. A structure as claimed in claim 22 in which the shunt between said center winding and said first end winding is larger than the other shunt.

24. A ballast for a lead-lag circuit and adapted to pro vide the ignition and starting voltages for a pair of gaseous discharge devices from an AC. source the voltage of which is substantially more than the operating voltages of said devices which comprises, an elongate iron core of generally shell construction having a center winding leg, three coils mounted on said winding leg, one in the center to provide a common inductor, the second on one end to provide a leading current inductor, and the third on the opposite end to provide a lagging current inductor, and with the second and third coils spaced from said first coil to provide shunts, the second coil shunt being smaller than the third coil shunt, connectors for connecting the leading current inductor in series with a capacitor, one of said gaseous discharge devices, and said common inductor, and for connecting the lagging current inductor in series with one of said gaseous discharge devices and said common inductor, the coils being arranged on said center winding leg so that the flux of said common inductor opposes the fluxes of said other inductors.

25. A ballast as claimed in claim 24 in which there is a gap in the core in the vicinity of said leading current inductor.

26. Apparatus for igniting and operating a pair of gaseous discharge devices and adapted to be connected across an AC. line which comprises, an elongate iron core, at least three inductive windings mounted on the said core, there being a center winding and two end windings, said core having first flux shunting means between said center winding and one of said end windings, and second flux shunting means between said center winding and the second of said end windings, the said first end winding having means comprising electrical leads for connecting one terminal of said one end winding in series with one of said gaseous discharge devices and to a terminal of said source, the second terminal of said one end winding being connected in series with at least a substantial portion of said center winding to the second terminal of said source, the second end winding having a condenser connected in series therewith, and having means including leads for connecting the same in series with the second of said gaseous discharge devices to said first terminal of said source, the second terminal of said second end winding also being connected in series with at least a portion of said center winding whereby at least a substantial portion of said center winding is common to the current flowing in both of said end windings, said center winding being so arranged on said core that its flux opposes the flux of each of said end windings whereby to create leakage reactance in both of said flux shunting means.

27. A lead-lag ballast for igniting and operating first and second gaseous discharge devices from a two terminal alternating current source comprising, a magnetically permeable core member, a first, end winding having first and second terminals, a second, central winding disposed about said core member and having first and second terminals, a third, end winding having first and second terminals, a capacitative reactance member, means connecting said central winding first terminal with a first terminal of said alternating current source, first conductive path means connected for establishing a first current path 1 7" J. -13 through at least a portion of said central winding, at least a portion of said first, end winding, and through said first gaseous discharge member to a second terminal of said current source, and second conductive path means connected for establishing a second current path through at least a portion of said central winding, at least a portion of said third, end winding, through said capacitative reactance member, and through said second gaseous discharge device to the second terminal of said current source in common with said first conductive path, wherein said first and third windings are connected and disposed about said core for generating a magnetomotive force in said core References Cited in the file of this patent UNITED STATES PATENTS 2,558,293 Feinberg June 26, 1951 2,585,963 Ranney Feb. 19, 1952 2,677,075 Campbell et al Apr. 27, 1954 2,885,597 Naster May 5, 1959 

